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| United States Patent |
5,216,037
|
|
Miyoshi
, et al.
|
June 1, 1993
|
Room temperature vulcanizable, foamable polysiloxane composition
Abstract
A room temperature vulcanizable, foamable polysiloxane composition is
described, which comprises:
(A) a specific type of .alpha., .omega.-dihydroxyorganopolysiloxane which
has a surface tension of not lower than 22 dynes/cm at 25.degree. C.;
(B) a specific type of organopolyhydroxypolysiloxane;
(C) a polyorganohydrogensiloxane which has at least two units of the
following general formula in one molecule
R.sup.5.sub.a H.sub.b SiO.sub.(4-(a+b))/2
wherein R.sup.5 represents a monovalent hydrocarbon group except for
aliphatic unsaturated hydrocarbon group, a is an integer of 0 to 2, and b
is an integer of from 0 to 3 provided that the total of a+b is an integer
of from 1 to 3;
(D) an unsubstituted or substituted alcohol having from 1 to 12 carbon
atoms; and
(E) a platinum catalyst.
The composition has a high degree of foaming and the foamed product
obtained from the composition has good foaming stability and good tensile
strength.
| Inventors:
|
Miyoshi; Kei (Annaka, JP);
Arai; Masatoshi (Annaka, JP)
|
| Assignee:
|
Shin-Etsu Chemical Co, Ltd. (Tokyo, JP)
|
| Appl. No.:
|
903308 |
| Filed:
|
June 24, 1992 |
Foreign Application Priority Data
| Current U.S. Class: |
521/88; 521/91; 521/92; 521/154 |
| Intern'l Class: |
C08J 009/02 |
| Field of Search: |
521/88,91,92,154
|
References Cited
U.S. Patent Documents
| 4461851 | Jul., 1984 | Hashimoto | 521/154.
|
| 4801622 | Jan., 1989 | Inoue et al. | 521/154.
|
| 4931485 | Jun., 1990 | Inoue et al. | 521/154.
|
| 4972001 | Nov., 1990 | Kimura et al. | 521/154.
|
| 5017624 | May., 1991 | Johnson | 521/154.
|
| Foreign Patent Documents |
| 33-9297 | Oct., 1958 | JP.
| |
| 44-8755 | Apr., 1969 | JP.
| |
| 45-9794 | Apr., 1970 | JP.
| |
| 45-12675 | May., 1970 | JP.
| |
| 51-46352 | Apr., 1976 | JP.
| |
| 59-45330 | Mar., 1984 | JP.
| |
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Lowe, Price, LeBlanc & Becker
Claims
What is claimed is:
1. A room temperature vulcanizable, foamable polysiloxane composition which
comprises:
(A) 100 parts by weight of an .alpha., .omega.-dihydroxyorganopolysiloxane
of the following general formula (I) which has a surface tension of not
lower than 22 dynes/cm at 25.degree. C.
HO--(SiR.sup.1 R.sup.2 --O).sub.1 --H (I)
wherein R.sup.1 and R.sup.2 may be the same or different and represent an
unsubstituted or substituted monovalent hydrocarbon group and l is an
integer of from 20 to 3000;
(B) from 0.01 to 30 parts by weight of an organopolyhydroxypolysiloxane of
the following general formula (II)
R.sub.3 SiO--(SiR.sup.3 R.sup.4 --O).sub.m --(SiR.sup.5
(OH)--O)--SiR.sub.3(II)
wherein R, R.sup.3, R.sup.4 and R.sup.5 may be the same or different and
represents an unsubstituted or substituted monovalent hydrocarbon group
except for aliphatic hydrocarbon groups, m is an integer of from 2 to 20,
and n is an integer of from 3 of 20 carbon atoms;
(C) a polyorganohydrogensiloxane which has at least two units of the
following general formula (III) in one molecule
R.sup.5.sub.a H.sub.b SiO.sub.(4-(a+b))/2 (III)
wherein R.sup.5 represents a monovalent hydrocarbon group except for
aliphatic unsaturated hydrocarbon groups, a is an integer of 0 to 2, and b
is an integer of from 0 to 3 provided that the total of a+b is an integer
of from 1 to 3, the polyorganohydrogensiloxane being used in such an
amount that the SiH group per unit mole of the hydroxyl group of the
ingredients (A) and (B) and an ingredient (D) is contained in the range of
from 0.5 to 20 moles;
(D) from 0.1 to 20 parts by weight of an unsubstituted or substituted
alcohol having from 1 to 12 carbon atoms; and
(E) from 0.1 to 200 ppm of a platinum catalyst, calculated as a platinum
metal, based on the total weight of the ingredients (A), (B) and (C).
2. The polysiloxane composition according to claim 1, wherein in the
formula (I), R.sup.1 is a phenyl group at a rate of 5 to 20% of R.sup.1
and R.sup.2 is a methyl group.
3. The polysiloxane composition according to claim 1, wherein in the
formula (II), R, R.sup.3, R.sup.4 and R.sup.5 are independently a methyl
group.
4. The polysiloxane composition according to claim 1, wherein in the
formula (II), R, R.sup.3, R.sup.4 and R.sup.5 are independently a phenyl
group.
5. The polysiloxane composition according to claim 1, wherein in the
formula (III), R.sup.5 is a methyl group.
6. The polysiloxane composition according to claim 1, wherein in the
formula (III), R.sup.5 is a phenyl group.
7. The polysiloxane composition according to claim 1, wherein in the
formula (III), when a is 2, R.sup.5 's may be the same or different.
8. The polysiloxane composition according to claim 1, wherein the SiH group
in the ingredient (C) is contained in an amount of from 2 to 10 moles per
unit mole of the hydroxyl group of the ingredients (A), (B) and (D).
9. The polysiloxane composition according to claim 1, wherein the
ingredient (D) is propanol.
10. The polysiloxane composition according to claim 1, wherein the
ingredient (D) is butanol.
11. The polysiloxane composition according to claim 1, wherein the
ingredient (E) is chloroplatinic acid.
12. The polysiloxane composition according to claim 1, wherein the
ingredient (E) is a complex of platinum and an olefinic compound.
13. A foamed product obtained from the composition defined in claim 1.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to foamable polysiloxane compositions of the room
temperature curable type which are improved in the degree of foaming and
foam stability.
2. Description of the Prior Art
As set out in Japanese Patent Publication No. 45-12675, several ways of
producing silicone rubber foamed articles at room temperature are known
including a method wherein foaming agents are added when room temperature
vulcanizable silicone rubber elastomers are obtained, and a method wherein
room temperature vulcanizable silicone rubber compositions undergo foaming
when cured or vulcanized. The latter method makes use of the
dehydrogenation reaction between organosilicon compounds having the
hydrogen atom directly joined to the silicon atom and organosilicon
compounds having the hydroxyl group directly joined to the silicon atom. A
number of catalysts for promoting the dehydrogenation reaction are known
in the art. For instance, Japanese Patent Publication Nos. 33-9297 and
44-8755 describe quaternary ammonium salts, carboxylates of heavy metals
and alkali metal alkoxides for use as the catalyst for the dehydrogenation
reaction, and Japanese Patent Publication No. 45-9794 sets forth
hydroxyamine compounds and organosilicon compounds having an aminoxy group
directly bonded to the silicon atom. In addition, platinum compounds are
taught in Japanese Laid-open Patent Application No. 51-46352.
However, the prior art foaming techniques are usually low in the degree of
foaming and poor in the foam stability, thus presenting the problem on the
improvement in heat insulation efficiency. Where the degree of foaming is
improved by the use of .alpha., .omega.-dihydroxyorganopolysiloxane with a
low degree of polymerization as set forth in Japanese Laid-open Patent
Application No. 59-45330, a disadvantage is inevitably involved in that
the silicone rubber foamed material has a low tensile strength.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a room temperature
vulcanizable, foamable polysiloxane composition which overcomes the
disadvantages of the prior art compositions and which has a high degree of
foaming and good foam stability.
It is another object of the invention to provide a room temperature
vulcanizable, foamable polysiloxane composition which has good mechanical
strengths such as a tensile strength.
The above objects can be achieved, according to the invention, by a room
temperature vulcanizable, foamable polysiloxane composition which
comprises:
(A) 100 parts by weight of an .alpha., .omega.-dihydroxyorganopolysiloxane
of the following general formula (I) which has a surface tension of not
lower than 22 dynes/cm at 25.degree. C.
HO--(SiR.sup.1 R.sup.2 --O).sub.1 --H (I)
wherein R.sup.1 and R.sup.2 may be the same or different and represent an
unsubstituted or substituted monovalent hydrocarbon group and l is an
integer of from 20 to 3000;
(B) from 0.01 to 30 parts by weight of an organopolyhydroxypolysiloxane of
the following general formula (II)
R.sub.3 SiO--(SiR.sup.3 R.sup.4 --O).sub.m --(SiR.sup.5
(OH)--O)--SiR.sub.3(II)
wherein R, R.sup.3, R.sup.4 and R.sup.5 may be the same or different and
represents an unsubstituted or substituted monovalent hydrocarbon group
except for aliphatic hydrocarbon groups, m is an integer of from 2 to 20,
and On is an integer of from 3 of 20 carbon atoms;
(C) a polyorganohydrogensiloxane which has at least two units of the
following general formula (III) in one molecule
R.sup.5.sub.a H.sub.b SiO.sub.(4-(a+b))/2 (III)
wherein R.sup.6 represents a monovalent hydrocarbon group except for
aliphatic unsaturated hydrocarbon groups, a is an integer of 0 to 2, and b
is an integer of from 0 to 3 provided that the total of a+b is an integer
of from 1 to 3, the polyorganohydrogensiloxane being used in such an
amount that the SiH group per unit mole of the hydroxyl group of the
ingredients (A) and (B) and an ingredient (D) is contained in the range of
from 0.5 to 20 moles;
(D) from 0.1 to 20 parts by weight of an unsubstituted or substituted
alcohol having from 1 to 12 carbon atoms; and
(E) from 0.1 to 200 ppm of a platinum catalyst, calculated, as a platinum
metal, based on the total weight of the ingredients (A), (B) and (C).
DETAILED DESCRIPTION AND EMBODIMENTS OF THE INVENTION
The respective ingredients which are essential in the composition of the
invention are now described.
The ingredient (A) is an .alpha., .omega.-dihydroxyorganopolysiloxane of
the general formula (I). In order to impart high mechanical strength to
the polysiloxane formed product obtained after curing of the composition,
the degree, 1, of the polymerization of the polysiloxane should be in the
range of from 20 to 3000. If the value of l is smaller than 20, the
resultant polysiloxane foamed product is not satisfactory with respect to
the elongation. On the contrary, the value of l exceeding 3000 is
unfavorable from the standpoint of handling. Preferably, the value of l is
in the range of from 300 to 2000. In the formula (I), R.sup.1 and R.sup.2
may be the same or different and represent an unsubstituted or substituted
monovalent hydrocarbon group. Examples of the monovalent hydrocarbon
groups include an alkyl group having from 1 to 6 such as, for example, a
methyl group, an ethyl group, a propyl group, a butyl group, a pentyl
group or a hexyl group, an aryl group having from 6 to 12 carbon atoms
such as a phenyl group, a naphthyl group or the like, and those groups
mentioned above but substituted with a halogen atom such as a chloromethyl
group, a 3,3,3-trifluoropropyl group and the like. In view of the ease in
availability and the surface tension, it is preferred that 5 to 20% of
R.sup.1 is a phenyl group and R.sup.2 is a methyl group.
The ingredient (B) is an organopolyhydroxypolysiloxane of the general
formula (II)
R.sub.3 SiO--(SiR.sup.3 R.sup.4 --O).sub.m --(SiR.sup.5
(OH)--O)--SiR.sub.3(II)
In the formula (II), R, R.sup.3, R.sup.4 and R.sup.5 may be the same or
different and represent an unsubstituted or substituted monovalent
hydrocarbon group as defined with respect to the ingredient (A). From the
standpoint of the ease in availability and the viscosity of the
composition, it is preferred that R, R.sup.3, R.sup.4 and R.sup.5 are each
a methyl group or a phenyl group. In the formula, m is an integer of from
2 to 30, preferably from 10 to 20 and n is an integer of from 3 to 20,
preferably from 5 to 20. If n is smaller than 3, the degree of foaming
undesirably becomes low, so that there cannot be obtained a room
temperature curable foaming polysiloxane composition which has a high
degree of foaming as intended by the present invention. When n exceeds 20,
the resultant foamed product is lowered in mechanical strength. The amount
of the ingredient (B) should be in the range of from 0.01 to 30 parts by
weight, preferably from 0.1 to 20 parts by weight, per 100 parts by weight
of the ingredient (A). If the amount of the ingredient (B) is less than
0.01 part by weight, the thixotropic properties of the resultant
composition are lowered, leading to poor foaming stability. Thus, there is
not obtained a foamed product which has fine cells or foams with good
foaming stability. When the amount exceeds 30 parts by weight, the
crosslinking rate becomes so lowered that the respective cells are
worsened in the shape.
The ingredient (C) used in the present invention has the hydrogen atoms
directly joined to the silicone atoms and such hydrogen atoms undergo the
dehydrogenation reaction with the hydroxyl groups directly boned to
silicon atoms to generate hydrogen gas and to form crosslinkage. The
ingredient (C) is a polyorganohydrogensiloxane which has at least two
units of the general formula (III) in one molecule
R.sup.5.sub.a H.sub.b SiO.sub.(4-(a+b))/2 (III)
In the formula (III), R.sup.5 is a monovalent hydrocarbon group including
an alkyl group having from 1 to 6 carbon atoms such as, for example, a
methyl group, an ethyl group, a propyl group, a butyl group, a pentyl
group or a hexyl group, an aryl group such as a phenyl group, a naphthyl
group or the like, and substituted hydrocarbon groups such as a
chloromethyl group, a 3,3,3-trifluoropropyl group and the like. If there
are a plurality of groups represented by R.sup.5, such groups may be the
same or different. In view of the ease in availability, R.sup.5 is
preferably a methyl group or a phenyl group. The hydrogen atoms directly
joined to the silicon atoms may be present at a terminal end or at a side
chain. The molecular structure may be linear, cyclic or branched. The
ingredient (C) is used in such an amount that the SiH group is contained
in the range of from 0.5 to 20 moles, preferably from 2 to 10 moles, per
unit mole of the hydroxyl group of the ingredients (A), (B) and (D). If
the amount is less than 0.5 moles, the degree of foaming and the foaming
stability are not improved appreciably. Over 20 moles, the resultant
foamed product does not become satisfactory with respect to the mechanical
strength.
The ingredient (D) is an unsubstituted or substituted alcohol having from 1
to 12 carbon atoms. This ingredient causes reaction with the ingredient
(C) in the presence of the ingredient (E) to generate hydrogen thereby
controlling the degree of foaming. Examples of the alcohol include
monohydric alcohols such as methanol, ethanol, n-propanol, iso-propanol,
n-butanol, iso-butanol, tert-butanol, 2-butanol and the like, and
polyhydric alcohols such as ethylene glycol, propylene glycol, glycerine
and the like. Examples of the substituted alcohol include those compounds
of the formulas, C.sub.2 H.sub.4 OC.sub.2 H.sub.4 OH, CH.sub.3 OC.sub.2
H.sub.4 OH and the like. Of these, propanol and butanol are preferred
because they are in good compatibility with the siloxane, are sufficient
for addition only in small amounts and are readily available. The amount
is in the range of from 0.1 to 20 parts by weight, preferably from 2 to 10
parts by weight, per 100 parts by weight of the ingredient (A).
Especially, in the range of from 2 to 10 parts by weight, there are
obtained the composition which ensures a high degree of foaming and also
the foamed product from the composition which has high mechanical strength
and good thermal stability.
The ingredient (E) is a platinum-based catalyst which promotes the
dehydrogenation reaction between the ingredients (A), (B) and (D) and the
ingredient (C). Examples of the ingredient (E) include metallic platinum,
chloroplatinic acid, complexes of platinum and olefinic compounds,
complexes of platinum and vinyl group-containing silanes or siloxanes, and
phosphite complexes of platinum. In view of the stability of the
composition prior to curing to which the ingredient (E) is added,
chloroplatinic acid and complexes of platinum and olefinic compounds are
preferred. The ingredient (E) is used in an amount of from 0.1 to 200 ppm,
preferably from 1 to 50 ppm, based on the total weight of the ingredients
(A), (B) and (C). If the amount is less than 0.1 ppm, the dehydrogenation
reaction proceeds only slowly. The amount over 200 ppm is poor in economy.
The foamable polysiloxane composition of the invention may further
comprise, as a diluent, polyorganosiloxanes which are blocked with a
triorganosilyl group at both ends or at one end thereof, and vinyl
group-containing silanes and siloxanes, if necessary, in amounts not
impeding the inherent properties of the composition. In addition, there
may be further used siloxane copolymers of the type represented by the
formula, (R.sup.7.sub.3 SiO.sub.1/2).sub.x (R.sup.8 SiO.sub.3/2).sub.y
(SiO.sub.2), other fillers, pigments, dyes, heat resistance improvers,
flame retardants and the like.
The present invention is more particularly described by way of examples.
EXAMPLES 1, 2 AND COMPARATIVE EXAMPLES 1, 2
An .alpha., .omega.-dihydroxyorganopolysiloxane (A-1) which had an average
structural formula, HO-(SiMe .phi.--O).sub.50 --(SiMe.sub.2 --O).sub.540
--H, wherein Me represents a methyl group and .phi. represents a phenyl
group, and which had a viscosity of 20,000 centistokes at 25.degree. C.,
an organopolyhydrogenpolysiloxane (B-1) of the average structural formula,
Me.sub.3 SiO--(SiMe.sub.2 --O).sub.5 --(SiMe(OH)--O).sub.10 --SiMe.sub.3,
wherein Me represent a methyl group, which had a viscosity of 150
centistokes at 25.degree. C., and a polyorganohydrogensiloxane (C-1) of
the average structural formula, Me.sub.3 SiO--(SiMe(H)--O).sub.38
--SiMe.sub.3, isopropyl alcohol (D-1) and an isopropyl alcohol solution
(E-1) containing 2% of chloroplatinic acid were provided and used to
prepared compositions of the examples and the comparative examples
according to the formulations indicated in Table. The respective
compositions were each subjected to foaming and curing to obtain foamed
products. The degree of the foaming and an average diameter of cells of
the foamed product were measured. The results are shown in Table below.
TABLE
______________________________________
Comp. Comp. Exam- Exam-
Ingredient Ex. 1 Ex. 2 ple 1 ple 2
______________________________________
Composition
(Parts By Weight):
A-1* 100 100 100 100
(surface tension)
(24.1) (24.1) (24.1)
(24.1)
B-1 1 5 1 5
C-1 20 20 20 20
D-1 0.5 48 6 5
E-1 0.5 0.5 0.5 0.5
H/OH (by mole)
20.8 0.4 3.15 3.34
Degree of Foaming
2 17.2 13.6 11.5
Diameter of Cells
0.1 0.8 0.1 0.1
(mm)
______________________________________
*Dyne/cm at 25.degree. C.
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